Add IBM J9 gc metrics

[amarziali]

IBM J9 garbage collector MXBeans differ from the openjdk ones since they have different policy and exposes mbeans with different names.

This PR adds new gc metrics for major and minor collections for all the supported gc policies (https://www.ibm.com/docs/en/sdk-java-technology/8?topic=options-xgcpolicy)

Jira Ticket: FRAGENT-1747

[mcculls]

LGTM

[carlosroman]

@amarziali Would this here be the Docker image to test these changes with?

[amarziali]

@amarziali Would this here be the Docker image to test these changes with?

Yes @carlosroman ! I can also suggest to act on -Xgcpolicy to change the gc policy in order to gather the metrics from different mbeans. Other than gencon being the default, I suggest having a try setting -Xgcpolicy:balanced. The other policies are a bit more unconventional and uses only major collections

[carlosroman]

@amarziali Thanks for the input. Can I check that this is what you expect to see as the metrics here?

[amarziali]

@amarziali Thanks for the input. Can I check that this is what you expect to see as the metrics here?

@carlosroman it looks ok. Sorry not having added those tests on this PR at this point. :) I imagine we can close this PR when the other will be merged

[carlosroman]

@amarziali Don't worry. I'll just add the tests as a separate PR to main. Have approved this and will merge it now.